Root rot of sweet peas
by Carl M Olsen
A THESIS Submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree
of Master of Science in Botany at Montana State College
Montana State University
© Copyright by Carl M Olsen (1957)
Abstract:
The soil-borne disease of sweet peas, which manifests itself as a root rot, was investigated in this study.
This work was primarily initiated to determine the causal organism and the predisposing factors
associated with the disease. Some of the work was also devoted to devising a means of control for this
disease.
Many isolations were made during the course of the study, from both cortical and vascular tissues of
diseased plants. In all cases species of Fusarium were obtained. Pathogenicity tests were conducted in
the greenhouse and in the laboratory with varied results. Three out of a total of thirty Fusarium cultures
were pathogenic in three pathogenicity tests, but non-pathogenic in one test, A mixture of 12 cultures,
including the three pathogenic ones, was also tested for pathogenicity, A moderate degree of
pathogenicity was. expressed in this test.
Three soil disinfecting materials were used for controlling root rot of sweet peas: Vapam 4-S (31%
sodium N-methyldithiocarbamate), CBP (chlorobromopropene), and Terrachlor (PCNB - 20%
pentachloronitrobenzene).
Sweet pea plots treated with CBP produced the largest proportion of healthy plants. This amounted to
65.3 and 63.5 per cent for 1955 and 1956 respectively. The check plots for the same years produced
55.9 and 46.6 per cent of healthy plants. The plots that were treated with Vapam produced 78.6 and
44.6 per cent healthy plants and the checks produced 31.4 and 15.4 per cent in 1955 and 1956
respectively. Plots treated with PCNB had 74.8 per cent healthy plants as compared with 49.1 per cent
in the checks. However, this compound was only used in 1956, ROOT ROT OF SWEET PEAS
A THESIS
Submitted to the Graduate Faculty
partial fulfillment of the requirements
for the degree of
Master of Science in Botany
Montana State College
Approveds
■tment
Chair
mini n g Committee
Bean, Grad^sg&K Division
Bozeman , -Montana
/0
OX.S\r
—
2—
ACKNOWLEDGMENT
Grateful acknowledgment is made to Dr. M. M. Afanasiev, who directed
this study and was most helpful in all its phases. The assistance of
Professor H. E. Mor r i s , Dr. I. K. Mills, Dr. H. S. MacWithey and other
staff members of the Department of Botany and Bacteriology, Montana State
College, is also greatly appreciated.
123693
3
- -
TABLE OF CONTENTS
ACKNOWLEDGMENT
2
ABSTRACT
4
INTRODUCTION
5
REVIEW OF LITERATURE
6
MATERIALS AND METHODS
9
EXPERIMENTAL PROCEDURE AND RESULTS
12
Pathogenicity Tests
12
Soil Treatments '
29
GENERAL DISCUSSION AND CONCLUSIONS
38
SUMMARY
41
LITERATURE CITED
43
ABSTRACT
'
The soil-borne disease of sweet peas, which manifests itself as a .
root rot, was investigated in this study.
This work w a s .primarily.ini­
tiated to determine the causal organism and the predisposing factors
associated w i t h the disease. Some of the work was also devoted to de­
vising a means of control for this disease,
. Many isolations were made during the course of the study, from both
cortical and vascular tissues of diseased plants.
In all cases species
of Fusarium were obtained.
Pathogenicity tests were conducted in the
greenhouse and in the laboratory with varied results. Three out of a
total of thirty Fusarium cultures were pathogenic in three pathogenicity
tests, but non-pathogenic in one test* A mixture of 12 cultures, in­
cluding the three pathogenic ones, was also tested for pathogenicity, A
moderate degree of pathogenicity was. expressed in this test.
Three soil disinfecting materials were used for controlling root rot
of sweet peas s Vapam 4--S (31% sodium N-methyldithio carbamate) , CBR
(chlorobromopropene), and Terrachlor (PCNB - 20%. pentachloronitr©benzene)
Sweet pea plots treated w i th CBP produced the largest proportion of
healthy plants, ,This amounted to 65»3 and 63*5 per cent for.1955, and
1956 respectivelyo The check plots for the same years produced 55*9 and
46,6 per cent of healthy plarits ,<> The plots, that were treated with
Vapam produced 78,6 and liU»6 per cent healthy plants and the checks pro­
duced S l 9Ij."and 15®Ii per cent in 1955 and 1956 respectively 0 Plots
treated wi t h PCNB had 7Iin8 per cent healthy plants as compared with li9<.l
per cent in the checks. However, this compound was only used in 1956,
=
5“
INTRODUCTION
The city of Bozeman was known in the past as "The Sweet Pea City",
This name was applicable as some of the highest quality sweet peas
(Latfayrus,odoratus L«) in the Northwest were grown in and around
Bozeman, Montana,
.An annual festival called the "Sweet. Pea Carnival"
was sponsored b y community service organizations until 1934.,
The fes­
tival consisted of parades of decorated floats and the presentation of
bouquets to passengers on trains passing through the town.
'
-
During this
:
time many homes and store-fronts were beautifully decorated with arrange­
ments of sweet peas.
In recent years the culture of sweet peas in Bozeman has gradually
diminished because of difficulties encountered in producing healthy
plants.
The Botany and Bacteriology Department of the Agricultural
Experiment Station, Montana State College, has received numerous inI
'
.
-
o
dairies from residents of the State, especially those living in Bozeman,
regarding the trouble in raising sweet peas.
Examination of diseased
specimens indicated that most of the difficulties in growing them were pro­
bably due to one..or morei,-soil-borne.,, root-rbt producing organisms 'which af­
fect the plants.
Since sweet peas are usually grown in a permanent bed,
it is likely that the continuous propagation in such locations brings
about a gradual build-up of the root rot pathogens.
The purpose of this
study was to investigate this disease, to identify the causal organisms
and to develop control measures.
-
6-
REVIEW GE LITERATURE
Root rote of sweet peas, caused b y various fungi, have been reported
b y several investigators,
Most of the, available literature merely re­
ports the incidence of the disease with very little description«,
Aphanomvces euteiches Drechs« root rot has been reported on the
perennial sweet pea (Lathvrus latifolius L.) in Wisconsin and on the
annual (Lc odoratus L«) in Indiana, Michigan, Wisconsin (8) and in
England (2)»
,Since
Aft euteiches
is a cortical tissue inhabit or, the
separation of the vascular cylinder: from the cortical tissues when
pulled f r o m the ground is a quick method of diagnosis of this disease,,
W o r k e r s in Massachusetts (8) have found Pvthium ultimum Trow to
>!'"
- ' '
'
'I
'
'
Drechsler (6), on
be an incitant of another root rot of sweet peas*
the other hand, reported .Pc oligandrum Drechsc to cause decay of mature
stems and roots, but only as a secondary organism*
Dodge and Rickett (5) and Taubenhaus (25) state that Rhizoctonia
s p p e and R 0 solani Kuhn are primarily damping-off ineitants, but also
cause root rot.
This root rot produces a characteristic constriction at
the limits of the infected tissues as the disease progresses u p the stem®
The roots are sparse and brown in color*
Post (19) states that R 0 solani-
and Fusariumrincited root rots are impossible to distinguish without
isolationse
Ascochyta lathvri Trail foot and root rot has been reported in
Argentina (11), England (12) and in Kansas (8) 0
Beaumont (2) reported
A® lathvri and its perfect stage, Mvcosphaerella oinodes Berk® and Blox0,
on sweet peas, but added it is "very rare"®
The symptoms of this disease
are striking and not easily confused with other root rots*
Tan, sunken
v
lesions w i t h dark brown margins m ay be found on the base of the stems*
Black, pin-point-sized pycnidia are often conspicuous in and around these
lesions*
Dimock (4) reported Verticil!Inm albo-atrum Reinke and Berth* on
sweet peas at Cornell University (Hew York)*
Taubenhaus (25) found Chaetomium spiroehaete Patt* on samples of rootrot-diseased sweet peas sent h i m from Cornell University and Illinois*
The root system is usually found to be completely or partly destroyed*
The disease seems to be primarily of a seedling infecting type.
Inocula­
tions of healthy Seedlings with pure, cultures of fungus proved the -.
organism to be weakly pathogenic, but the pathogenicity is favored by an
excess of soil moisture*
A root rot incited by Thielavionsis basicola Brierley has been r e - .
ported as occurring on sweet peas generally throughout the United States,
_ especially on the. Pacific Coast (8) and in Holland (13)«
In Holland, the
V
abnormal "soil sickness" is caused b y this organism and is responsible
for heavy losses in Dutch sweet pea crops.
on sweet peas-are quite Variable*
The symptoms of this disease
In severe cases, delayed growth is a
conspicuous feature and the plants do not exceed 15 to 30
The roots are dark brown and much reduced in length.
cm, In height*„
The formation of ad­
ventitious roots retards the death of the p l ants, which is preceded by
gradual wilting*
Pfeny individual plants harbor the pathogen without show­
ing noticeable external symptoms,
Mooi-Bok (13) states that the fungus
has never been detected within the central cylinder or endodermis of even
™3“
heavily infected plantse
According to Taubenhaus (24) and Bodge and
Bickett (5) Thielaviopsis root rot can be easily distinguished b y the
stubby, charred appearance of the rootse
An insufficient amount of work has been done on the root rot of
sweet peas which is incited b y Fusarium specieg.
.The .occurrence of. this
disease has been reported only in a few cases. ,Taubenhaus (24, 25) re­
ported Fusarium wilt to be incited by F. Iathvri Taub..
good account of general symptoms of this disease.
He also gave a
Dodge and Rickett (5)
also state that Fusarium root rot of sweet peas is due to infection by
JT0 lathyri Taub..
Workers in N e w York and Florida (8) reported F u s a r i m
spp. as causing stem rot, root rot and wilt.
,The isolation of Fusarium
spp. from sweet peas affected with root rot has been reported in
Victoria, B. C. (18).
No attempt was made to identify the organism any
further in this instance.
.Beaumont (2) reported the isolation of F.
culmorum (Smith) Saccardo from root-rot diseased sweet peas in England.
MATERIALS A ND METHODS
A n attempt was made to isolate and to. prove pathogenicity of the or­
ganism or organisms responsible for the root rot of sweet peas, _Isolations
of fungi were made from diseased sweet pea plants grown in resident-owned
plots in and around Bozeman, Montana,
Diseased plants were removed from
their plots and brought to the laboratory.
The roots were washed and
bits of diseased vascular dr cortical tissue were placed on water agar
:
(2%),
Hyphal-tip transfers were made to Potato-Dextrose-Yeast (PDY)
medium.
This is standard PDA medium with 2 gt, of yeast extract (Difco)
added per liter.
Thirty cultures of fungi were isolated in this manner.
These cul­
tures were allowed to sporulate on three per cent PDY medium and then
examined microscopically to identify them,
.They were next put into nine
groups, on the basis of their macroscopic similarities, to facilitate
handling.
Single spore isolations of the above.cultures were made and the re­
sulting cultures were tested for pathogenicity.to sweet peas in the
greenhouse and in the laboratory,
In an attempt to find a means of control of the root rot disease of
sweet peas, a number of sweet pea plots in Bozeman, known to produce dis­
eased plants, were selected for treatment,■ The soil in each of these
plots w a s treated w i t h one of the three following soil fumigants,
Yapam
Ik-S
(31%
Sodium N-methyldithiocarbamate dihydrate)
J
'
Application-. 15,2 ee per square foot diluted in water and sprink­
led on the soil surface, '
-
10-
FropertiesSolubility- readily soluble in water (72*2 g,,-per 100 cc at 20°
Cri) j, moderately soluble in alcohol, sparingly
soluble in other common organic solvents*
Phvtotoxic i t y - known to be damaging to roots of established
plants and to cause foliage damage by fumes*
CBP (I - chloro-3"bromopropene-l)
(OS-840 technical chlorobromdpropene)
Application- 1*5 cc per hole spaced one foot apart* A satisfac­
tory hole was made b y plunging a one inch diameter,
pointed stick into the ground at the prescribed
distance to a depth of six inches*
Optimum soil
temperature for this treatment is 60oF* and soil
moisture 50% equivalent moisture (45“ 70°F* and 2070%) *
PropertiesSolubilitv- highly soluble in high hydrocarbon solvents, less
soluble in water*
Phvtotoxicity- Phytotoxicity can be reduced somewhat by
shallow planting methods, b y the time of ap­
p l i c a t i o n , and b y diluting the chemical*
Porous and drier soils also help reduce the
toxicity*
PCRB- (Terrachlor)
(20% pentachlor©nitrobenzene)
Application- 200 pounds of active dust per acre or 0*0046
pounds per square foot*
The dust was merely worked into the soil to a
depth of about six inches*
PropertiesSolubilitv- soluble in acetone, benzene, toluene, and xylene*
Slightly soluble in methyl, ethyl &nd. isopropyl
alcohols*
Phvtotoxicity- considered safe for use in treating soil (at
50-200 lb* active chemical per acre) just
prior to or at the time of planting of most
crops*
The application rates of all three materials were made according to
the manufacturer}s recommendations*
-
11-
The sweet pea seeds used in these tests were obtained from George J e
Ball, Chicago, Illinois,, with the exception of one Burpee Seed Company
variety.
Eleven varieties, all summer flowering, were used in the field plots*
These varieties are:
I*
Ball White-white seeded
(21982-83)
2,
Snow White-black seeded
(2142-24)
3.
White Blush
;
4«
Guthbertson Strain, Janet
5,
Ruffles
6,
Fiesta- Scarlet
7,
Welcome- Scarlet
8,
Geo, j* Ball- Coral Rose
9o
Rose-pink
(3667-103)
(14047-115)
(Burpee) ....
(165-83)
(12147-14)
(31437-93)
(3697-103)
10,
Ball Blue Supreme
(11995-111)
11,
Cuthbertson Strain, Jimaay
(11757-103)
These varieties were planted in three groups composed of four varie­
ties each.
Each plot was planted with one group (i,e, four varieties) in
two rows parallel to the length of the plot.
deep and spaced one inch apart.
planting.
each plot.
The seeds were planted ■§- inch
All seeds were Arasan-^treated prior to
The same .planting plan was followed in the check portion of
—
12=*
EXPERIMENTAL PROCEDURE AND RESULTS
Pathogenicity Tests
Isolations of fungi were made from diseased sweet pea plants through­
out the 1955 growing season.
ThSse plants usually grow normally in the
beginning of the season, but as soon as they begin to bloom a yellowing
of the lowest leaves is evident.
This yellowing gradually becomes exten­
sive and is followed b y a reddish-brown discoloration of the vascular
system which is continuous from the tip of the roots to a height of one
to two inches above the soil line.
The root system is reduced to several
dark colored laterals and a short, darkened tap root.
In some cases,
plants less severely infected frequently produce new lateral roots above
the discolored portion of the tap root.
shorter than normal.
These laterals are thicker and
The infected plants n ay continue to grow until the
flower buds begin to open, even though the lower leaves show firing.
this time, the plants are usually rapidly killed.
At
Often infected plants
appear stunted and unthrifty in growth, and these may die long before
\
bud formation,
In some cases, seedlings only three to six inches in
height will succumb when severely infected.
The final symptom of this
disease is a complete desiccation of the plant.
In making isolations, diseased plants were removed from the plots,
their location recorded, and brought to the laboratory.
The roots were
then washed in mild soapy water and placed in tumblers covered with
cheese cloth.
Gold tap water was circulated through the jar for two to
three hours, followed b y several sterile water rinses.
This procedure
helped to reduce bacterial organisms which were present on the roots as
-
contaminantso
13-
Bits of diseased vascular or cortical tissue were placed in
Petri dishes containing water agar (2%) for fungus isolation*
was used to reduce bacterial contaminants*
Water agar
Hyphal-tip transfers were
made to Potato-Dextrose-Yeast (PDY) medium which was used as a standard
medium for sporulation and growth throughout the experiments*
In an attempt to eliminate the growth of bacteria present as con­
taminants, lactic acid was added to the w a r m medium in sufficient amounts
to lower the pH to approximately 4 ° 0 o
It was observed that acidifying the
medium to this extent reduced the fungus growth rate somewhat and made
zonation of the colonies more prominent and closer together*
The re­
tardation of the growth depends on the kind of acid and its concentration
according to Smith and Swingle (21)*
Lewis (10) states that different Fus=
a r i u m 'species are not affected to the same degree, some tolerating more
acid than others*
Seventeen cultures of Fusarium were isolated in this manner from
diseased plants grown in treated and check plots during the summer of
1955 and tested for pathogenicity*
Thirteen other cultures of Fusarium*
isolated b y M* M* Afanasiev, Montana State College, during 1953-1954 were
also evaluated for pathogenicity*
These 30 cultures of fungi were inocu­
lated onto PDY medium w i t h three per cent agar in test tubes*
Slotted,
open-faced test tube racks were devised to support these tubes at a
45 degree angle*
The racks and tubes were placed in diffuse natural
lighting and maintained at r o o m temperature to induce sporulation*
Several
weeks later, these cultures were examined microscopically and all appeared
to belong to the genus Fusarrum*
-
14“
The genus Fusarium belongs to the order Moniliales 9 the family Tubercuifceae and the section Pharagmosporae 0
This genus has sporodochiai> core-
mial or pionnptal type fruiting bodies ? however a t r u e ■coremium was not
observed in a n y of the cultures isolated in this study,
SherbakOff (20) also
did not observe a true coreaial fructification in his work.
Two definite
and distinct types of fructification were seen in this study on numerous
occasionse
The most common fruiting structure observed in this study was
a continuous mass' of Sporess, together with their Conididphores5, heaped up
into a wart-like Structure known as a Spbrodochiume
The second type of
asexual fruiting structure observed is called a pseudOpionriote'Sj, which
resembles a true pionnotes in appearance, but differs in origin according
to Sherbakoff (20)„
This structure originates from the production of
minute and numerous spbrodochia very close to or on the substrate Sur­
face, so that they then form a nearly continuous, slimy layer of Conidiae
The following characteristics, as outlined b y Sherbakbff (20),■ were
noted on the isolated culturess
macroconidial and mleroeonidial size,
septatibns, morphology, and prevalence; chlar^rdoSpbre prevalence and mor­
phology,
Ten conidia, or ten chlamydospores, were measured and the
averages of these measurements were recorded*
In case of special variabi- ■
I i t y of the material, records were made of 15 or
20
spores*
,These isolates were placed in nine groups separated1on the basis of
similarities in medium discoloration, size and shape of conidia, color of
mycelium, and amount of surface or aerial growth*
Group I-
Whitish-gray mycelium with yellowish macroconidial masses;
little aerial growth, no medium discoloration*'
-
15-
macroconidiamicroconidia-
33.6
x
6 .2u,
9.3 x A.Op to 18.6 x
6 .2p.
x
5.5y
to
60.0
Culture n u m b e r s :
10, 11, 26-A, AO, A5, 51, 52
Group II-
Whitish-gray mycelium with bluish macroconidial masses;
little aerial growth; and no medium discoloration,
macroconidia- 2A.8 x A. 6p to 5A.0 x 5.5p.
microconidia-
11.6
x 3.9p to 22.5 x
5.8p.
Culture n u m b e r s :
21, 3A-A
Group III- Whitish mycelium; moderate aerial growth; purplish to
reddish medium discoloration.
macroconidia- 31.0 x
microconidia-
6 .2p
to A3.A x
6 .2p.
8.0 x 3.5p to 2A.8 x A. 6p.
Culture numbers:
U,
Group IV-
22,
2A
Whitish-gray mycelium; little aerial growth; purple medium
discoloration.
macroconidia- 21.5 x
microconidia-
6.2
6 .Ip
to AO.O x 6.5p.
x A.5p to 21.3 x A. 6p.
Culture numbers:
15, A7
Group V-
White mycelium; moderate aerial growth; no medium discolora­
tion.
macroconidia- 29.0 x A.Qp to Al.5 x
5.8p.
16-
-*
mi croc onidiaCulture numbers
6.4
x 3.3p to
21.2
x
4 .6)1.
s
12, 23, 34-B, 34-C, 46, 50
Group VI-
White mycelium? moderate aerial growth with orange tinged
macroconidial masses? no medium discoloration,
macroconidia- 32.5 x
microconidiaCulture numbers
9.3
x
4 .6)1
to 47.5 x
5.6)1.
2.^i
to 15.5 x
3 .Ip.
s
13, 26-B, 33-A, 33-B, 42
Group VII- Whitish-gray mycelium; moderate aerial growth? dirty
yellow occasional macroconidial masses? no medium dis­
coloration? burnt orange color at junction of aerial
mycelium and agar.
macroconidia-
24.8
x
6 .2p
to
25.6
x
5.5p.
microconidia- rare
Culture n u m b e r s s
35, 43
Group VIII- Whitish-gray mycelium? little aerial growth? dirty
yellow to bluish macrospore masses? no medium discolora­
tion.
macroconidia- 22.2 x
4 .6)1 to
microconidia-
3 .6p
Culture numbers
9.3 x
52.7 x 5.2p.
to 16,5 x
4 .2p.
s
25, 44
Group IX-
Whitish mycelium with pinkish cast? much cottony aerial
-
17-
growthI bright purple medium discoloration*
ma c r o conidia- 56*4 x
4 «2p
to 58*9 x
4 o 6ji*
mi c r o conidia- none
Culture n u m b e r s
49
Single spore isolations were made b y a serial dilution method*
this technique, a wire loop
5
m m in diameter was used to transfer spores
from an aqueous suspension to t u b e s ■containing
wa t e r agar.
For
10
cc of melted, lukewarm
The spore dilution series was completed b y transferring four
'I'bop-fulls successively-from one tube to the next*
and spores was poured into sterile Petri dishes*
A thin film-'of agar- '
After 24 to 36 hours
# h e plates were examined b y inverting them on a microscope stage and
viewing through the agar w i t h low power (IOOx)»
germinating maeroconidium could be found*
By this procedure, a
After marking its position
with a dot of.India ink on the bottom of the dish, an agar disk includ­
ing the spore was cut out' and transferred to a Petri dish of. PDY medium*
A t least six single spore isolations were made from each Fusarium iso­
late to reduce the chance of overlooking a mixture of two or more
Fusaria*
Sherbakoff (20), in his classic works on the Fusaria, found
this procedure worth while in only a few cases*
However, in one in­
stance, he isolated a pink fungus which on dilution gave rise to a brick
red Fusarium and a white one*
In three weeks time the six single spore isolations' of each culture
were compared*
A letter such as A or B was added to the culture number
of any variants occurring and they were treated as a distinct culture,
"
18"
for example 34”A and 34” Bo
The following method for testing pathogenicity of the isolated
teoltures;Jwas m s e ’di'in'^the^greenhousekm-.'.'Eight"inch■'pots,containing.
_•
three parts soil to one part sand were sterilized in an autoclave for
three h o u r s 5 under 15 pounds pressure in sufficient number for four ap­
plications of each culture to be testedo
Twelve seeds of Janet variety
were planted in each pot and the soil surface was covered w i t h a oneeighth inch layer of sterile Sande
A trellis, simply constructed of
' •
J
bamboo poles and string, was used to accommodate the climbing nature of
the sweet pea plants (see Figure I ) »
;
S
One of the single spore cultures, representing the parent type in
each series o f six tubes, plus any variants that occurred, were selected
to prepare the ino Culum 0
A suspension of each culture was made in ster­
ile water blanks and enough of this suspension was poured into a Petri
dish to barely cover the hardened.PDY medium®
After 10 to 14 d a y s .the
surface growth was used as Inoculum 0 Water suspensions of these cultures
were agitated briefly in a Waring Blendor and applied to the surface of
the sterilized soil, at the rate of two dishes per p o t 0
The soil was
inoculated w h e n the young sweet pea plants were one to three inches
high (see Figure 2)»
It was found that inoculations at the time of;
seeding produced too poor a stand as most of the radicles of the germina­
ting seeds were severely attacked b y the Organism 0
Also, it was noted
that the Fusaria colonized the seed coat to produce a whitish mass of
mycelium enclosing the entire germinating seed*
.Weekly readings were taken and isolations were made from the diseased
-
Figure I 0
19-
Pathogenicity test IV showing plants nearly at maturity and
trellis system
-
Figure 2.
20-
Sweet pea seedlings at stage of inoculation
“
21“
plants as previously described*
The newly isolated cultures were compar­
able to the original ones* „
Several pathogenicity tests were run using the same cultures to
eliminate possible variation in procedure and to check on the possibility
of loss of virulence in culture through variability from the parent type*
Investigations on the variability of Fusaria in cultures is a.fairly re“
cent and rapidly growing field of study*
general types of growth*
Oswald (17) observed two
The first is of abundant aerial mycelium and
with conidia produced in sporodochia*
The second is of suppressed aerial
growth and the conidia are produced in pseudopionnotes *
the culture has a slimy texture *
The surface of
He also observed that all cultures re™
presenting the first type produced mutants of the second*
Some of the
variants were changed to such an extent they fell into different species
or sections than their parents*
He also found that cultures forming
pseudopionnotes were generally less pathogenic on their respective hosts*
Results of the work reported here indicated that all of the cultures
wh i c h showed a degree of pathogenicity were in Oswald’s type one*
Other
investigators, such as Buxton (3), Snyder (23), and Armstrong and
Armstrong (I) noted culture variations and biological races in isola­
tions of Fusaria from peas and related genera*
Cultures 4 9 y 43, and 33"A showed a moderate degree of pathogenicity
in three consecutive trials (see Tables I, II, and IV)*
In Test III,
h o w ever, these same cultures expressed no pathogenicity (see Table III)*
A fifth test consisted of a mixture of 12 cultures, including the three
pathogenic ones and this culture mixture showed a moderate degree of
-
Table I.
22-
Pathogenicity Test I, showing the number and percentage of
healthy and diseased plants.
Culture
Number
43
Replication
Number
Sweet Pea Plants
Numbers
Percentage
Healthy
Diseased
Healthy.
Diseased
I
2
2
I
3
0
4
4
4
I
2
3
3
4
5
4
2
I
3
2
2
0
0
4
6
3
I
8
2
4
4
3
Average
42.8
66.7
100*0
^ O O
57.2
33.3
ffi
Average
Check
o.o
66.7
80.0
3
Average
33-A
20.0
20.0
Average
49
33.3
0
0
0
60.0
0.0
40.0
-OtQ
100.0
100.0
20.0
80.0
100.0
100.0
100,0
100.0
0.0
0.0
0.0
0.0
-
Table II.
23-
Pathogenicity Test II, showing the number and percentage of
healthy and diseased plants.
Culture
Number
Replication
Number
43
I
6
2
5
3
4
3
6
2
Sweet Pea Plants
Numbers
Percentage
Healthy
Diseased
Healthy
Diseased
Average
2
6
8
2
3
3
3
I
49
I
Average
33-A
Average
85.7
80.0
50.0
73.9
33.3
44.4
21*0
3lt.6
14.3
20.0
I O iO
26.1
I
6
2
5
I
3
85.7
62.5
14.3
37.5
3
6
2
11*0
25,0
73.9
26.1
Average
Check
66.7
55.6
71,0
65.lt
I
4
2
8
3
5
0
0
0
100.0
100.0
100.0
100.0
0.0
0.0
0,0
0.0
-
24-
Table III.
Pathogenicity Test III, showing the number and percentage of
healthy and diseased plants.
Culture
Number
Replication
Number
43
I
8
2
13
3
11
I
2
9
7
3
10
I
12
2
13
3
11
I
2
10
10
3
9
Sweet Pea Plants
Percentage
Numbers
Healthy
Healthy
Diseased
Diseased
0
0
0
100.0
100.0
100.0
100.0
0.0
0.0
0.0
0.0
0
0
0
100.0
100.0
100.0
100.0
0.0
0.0
0.0
0.0
0
0
0
100.0
100.0
100.0
100.0
0.0
0.0
0.0
0.0
0
0
0
100.0
100.0
100.0
100.0
0.0
0.0
0.0
0.0
Average
49
Average
33-A
Average
Check
Average
-
Table IV.
25-
Pathogenicity Test IV, showing the number and percentage of
healthy and diseased plants.
Culture
Number
Replication
Number
43
I
Sweet Pea Plants
Percentage
Numbers
Healthy
Diseased
Healthy
Diseased
10
11
11
11
2
3
4
I
90.9
9.1
0
100.0
0.0
I
91.6
0
100.0
95.8
8.4
O iO
4.2
3
I
70.0
90.9
30.0
9.1
0
0
100.0
100.0
0.0
0.0
90.9
9.1
Average
49
I
7
2
10
12
11
3
4
Average
33-A
I
2
3
4
11
12
12
I
91.6
8.4
0
100.0
0.0
I
92.3
13
0
100.0
96.0
7.7
O aO
4.0
11
12
12
10
0
0
0
0
100.0
100.0
100.0
100.0
100.0
Average
I
42
2
3
4
-
Average
Check
I
2
3
4
Average
10
10
11
12
0
0
0
0
100.0
100.0
100.0
100.0
100.0
0.0
0.0
0.0
O aO
0.0
0.0
0.0
0.0
4aQ
0.0
26=
“•
pathogenicity (see Table V ) »
Soil temperatures which were taken during the pathogenicity tests in
the greenhouse showed that the degree of pathogenicity varied with the
soil temperature*
The greatest pathogenicity was expressed at a soil
temperature of 28°Q*
The soil moisture was reduced to help increase the
soil temperature and to provide more favorable conditions for the develop­
ment of the organism*
This temperature agrees with that found b y Walker
(28) and Tisdale (27) in their studies with Fusarium*
The lack of patho­
genicity at lower soil temperatures was especially evident in Test III
(see Table III)*
The soil temperature during this test averaged 19°C,
with the maximum 20°G and the minimum 18,50G*
.During Tests I and IIjl in
which the highest pathogenicity was shown, the temperature ranged from.
)
25*5° to 28*50C *
In Test. IV, where moderate pathogenicity was ,expressed
I
(see Table I V ) , the temperature averaged 24«5°C*
v
The three cultures which were found to be pathogenic w e r e ■identified
w i t h the use of Gilman.?s (7)=, Sherbakoff tS (20), Snd iWollenweber and
Reinking-tS (29) keys*
section Roseum*
Cultures 33™A and 49 appeared to be members of the
Culture 43 keyed out to the section Elegans*
Confirma­
tions of the identifications were made b y H 0 S* MaeWithey, Montana State
"
i .
College *
Several laboratory methods for determining relative pathogenicity of
the different isolates were tried*
The method found most satisfactory was
a modification of the technique described b y Neergaard (15) and Kilpatrick
et al« (9)»
It consisted of aseptically growing seedlings in combination
w i t h F u s a r i u m OzTfIlter paper" platforms suspended in ste"rlle~distiiled
-
Table V.
27-
Pathogenicity Test V, inoculated with 12 cultures including the
three pathogenic cultures, showing the number and percentage of
healthy and diseased plants.
Treatment
Replication
Number
Inoculated
Sweet Pea Plants
Percentage
Numbers
Healthy
Diseased
Healthy
Diseased
I
9
2
10
10
11
3
4
I
I
2
I
Average
Non-inoculatedI
I
2
Average
11
12
0
0
90.0
10.0
90.9
83.3
91.6
88*9
9.1
16.7
8.4
100.0
100.0
100.0
0.0
0.0
0.0
11.1
“ 28“
water in test tubes#
The platforms were prepared as follows s
sterile
filter paper disks were shaped around the open end of a test tube to form
a cylinder with one end closed#
This cylinder was then inserted into the
tube w ith the closed end, or platform, nearest the mouth of the tube#
Sterile water was added to bring the level about one-fourth inch below
the. platform#
Five seeds, surface sterilized in 50 per cent Purex for ten minutes
and washed several times in sterile water, were placed on the platform and
the test tubes were stoppered w ith cotton#
A small block of medium was
cut from a Petri dish containing one of the single spore cultures and
placed in the center of the ring of five seedlings when they were about
one inch high#
The tubes were then set into vertical test tube racks in
natural light and maintained at room temperature#
cultures 43,
.49, 33" A., 10
and
40
Three replications of
plus three checks were run in this exper/
iment#
The tubes were examined daily until the seedlings were about six
inches high#
At this time, they were removed and isolations were made
f r o m diseased tissues#
A discolored brownish region on the radicle was noted, presumably due
to infection'by the Fusanitim. isolates# This zone wad usually about -one’cen­
timeter below the location of the cotyledons#
The epicptyls of seedlings
1
upon whose radicles this discoloration was evident showed little abnor­
mality#
In exceptional cases, the lowest leaves wilted and dried up, "
but the plants appeared to recover#
In most cases new lateral roots were formed above and below the dis­
colored region#
Examination of longitudinally split primary roots showed
-
29-
a reddish-brown discoloration in the vascular system, but this did not
appear in n ewly formed laterals.
This reddish-brown streak extended from
the r egion of surface discoloration down to the root tip.
The vascular
discoloration in some plants extended u p the epicotyl to a position com­
parable to about one inch above the soil line.
The plants were killed
when this occurred.
Isolations were made throughout this experiment and cultures of
Fusarium obtained were compared w i t h the original cultures.
the criteria of comparison were identical.
In all cases
It was of interest to note
that all successful isolations of Fusarium were made from the main roots
showing the reddish-brown vascular discoloration.
No successful isola­
tions were made from the new laterals.
Soil Treatments
A total of twelve resident-owned sweet pea plots were used in 1955,
for studying the disease (see Figure 3).
in size.
These plots averaged 12 x 2 feet
A two-foot check portion, at the end of each plot, was separated
from the rest b y sinking a galvanized iron sheet across the plots to a
depth of t en inches.
A trellis was constructed for each plot by driving an eight-foot
pipe into the ground at the ends of each plot.
A wire wa s attached to
each pipe and on the wire "Train-etts” , a nylon net trellis manufactured
b y Germains of Los A n g eles, California, were suspended.
The larger portions of seven plots
with GBP.-
were treated w i t h Vapam and five
Vapam was applied at the rate of 15.2 cc of concentrate per
square foot, diluted in two gallons of water and sprinkled on the soil
-
Figure 3.
30-
Sweet pea plot at the Bole's residence, showing the contrast
between the check and Vapam treatment (1955)#
-
surface*
31^
CBP was applied at the rate of 1,5 cc of concentrate per hole
in sixrinch holes spaced one foot apart*
Approximately one gallon of
water per three square feet of treated soil was added as a seal, on both
of these soil fumigants.
The plots were treated on May 12, 1955«
The soil was cultivated
several days before and eight days after treating.
All plots were seeded
ten days after .the treatment* '■ This delay was necessary to allow for .dis­
sipation of the chemicals*
All of the Vapam treated plots except one had to be replanted due to
poor stands.
This probably resulted from the residual effect and high
toxicity of the chemical, ‘,None of the plots.treated with CBP required
replanting.
During October, 1955, a total of 14 sweet pea plots were cultivated
and treated in the same manner as in the previous spring.
The fall treat­
ment was made in an attempt to eliminate the problem of toxicity of the
materials to the sweet pea seedlings.
In addition to the increase of the
number of plots, another soil fumigant was employed for the
1956
tests,
Terrachlor (PCNB) was applied according to the manufacturer fs recommen­
dations*
The application rate was 200 pounds of active dust per acre, or
0,0046 pounds per square foot.
This chemical was worked into the soil to
a depth of about six inches, but no water seal was applied.
Since sweet peas had been grown in these plots for a number of years
and the sweet pea vines commonly removed, it was thought that the organic
level and fertility of the soil would become low.
For this reason a
source of organic matter, Milorganite, was applied prior to any chemical
“
32-
30
soil treatment at the rate of
pounds per
and prepared seedbeds in the fall of 1955o
100
square feet to the spaded
Milorganite appeared to in­
crease the vigor of the plants as some were over ten feet in height (see
Figure 4)=
The soil was cultivated and Milorganite added on October 3 and
The next day the plots were treated.
6, <1955»
The following spring, M a y 9, 1956,
the soil was cultivated once a^ain and planted to sweet peas*
The planting plan in 1956 was. slightly different from that of 1955*
One complete row of Janet, a relatively susceptible variety, was planted
in the treated portion in each plot*
were planted in the checks*
Two parallel rows of the same variety
Parallel to the white Janet variety, three
colored varieties, Jimmy, Tommy, and Lois, were planted in the treated por?
tions solely for appearance*
Readings were taken throughout the season"'"
on the Janet plantings*
In 1955, plots treated w i t h Vapam (Table VI) and CBP (Table VII)
produced 78*6 and
65*3
per cent healthy plants whereas the checks produced
only 31»U and 55,9 per cent respectively*
The results of the 1956 soil
treatments, given in Table VIII, show that Vapam-treated plots produced
y i „6 per cent while CBP plots produced 63.5 per cent healthy plants*
The respective checks had l S M
treated plots produced
74«8
and 46*6 per cent healthy plants.
per cent and the checks
1|9 .1
PCNB-
per cent healthy
plants (see Table V I I I ) , however this chemical was used only one year*
The results of the soil treatments with the three'chemicals for/1955 and.
1956.are compared in Figure 5«
-
-
Figure 4
33-
Sweet pea plot at the Hartman residence.
over ten feet high (CBF-1956).
The plants are
-
Table VI.
34-
The effect of Vapam soil treatment on the incidence of sweet
pea root rot for 1955.
Sweet Pea Plants
Numbers
Variety
I
I
I
Plot
Check
H
D
Percentage
Treated
H
D
Check
H
Treated
D
H
D
Taylor
Bole
DeFrate
(South)
5
I
4
8
22
21
3
12
55.5
11.2
44.5
88.8
88.0
63.6
12.0
36.4
I
4
27
3
20.0
80.0
90.0
10.0
DeFrate
(South)
I
3
25
6
25.0
75.0
80.6
19.a
I
2
25
3
33.3
66.7
89.3
10.7
5
3
16
9
62.5
37.5
64.0
36.0
4
Morris
(West)
Hartman
I
0
7
I
17
17
3
11
12.5
0.0
87.5
100.0
85.0
60.7
15.0
39.3
5
5
Taylor
Bole
3
2
7
8
18
32
5
0
30.0
25.0
70.0
75.0
78.3
100.0
21.7
0.0
6
6
Hartman
Morris
(West)
2
2
15
13
50.0
50.0
53.6
46.4
I
6
12
9
14.3
85.7
57.1
42.9
7
7
Taylor
Bole
2
0
8
10
22
26
3
6
25.0
0.0
75.0
100.0
88.0
81.2
12.0
18.8
8
DeFrate
(South)
4
4
27
2
50.0
50.0
93.1
6.9
Morris
(West)
Hartman
2
2
5
0
19
16
8
10
28.6
100.0
71.4
0.0
70.4
61.5
29.6
38.5
Taylor
Bole
5
2
5
5
21
17
0
9
50.0
28.6
50.0
71.4
100.0
65.4
0.0
34.6
43
_2
94
_26
421
__ I
116
60*p
31.U
40.0
68,6
Mil
78.6
MiZ
21.U
2
3
3
4
9
9
10
10
11
Hartman
Morris
(West)
DeFrate
(South)
Totals
“
Table VII.
35-
The effect of CBP soil treatment on the incidence of sweet
pea root rot for 1955.
Sweet Pea Plants
Numbers
Var­
iety
Plot
Check
H
D
Percentage
Treated
H
D
Treated
Check
H
D
H
D
I
I
Morrison
Parker
6
6
3
3
26
7
12
14
66.7
66.7
33.3
33.3
68.4
66.7
31.6
33*3
2
Parker
0
8
16
12
0.0
100.0
57.1
42.9
3
DeFrate
(North)
Morris
(East)
6
2
19
7
75.0
25.0
73.1
26.9
4
I
4
11
80.0
20.0
26.7
73.3
3
2
14
7
60.0
40.0
66.7
33.3
5
3
8
7
62.5
37.5
53.3
46.7
5
3
35
10
62.5
37.5
77.8
22.2
3
4
4
DeFrate
(North)
Morris
(East)
5
Morrison
6
DeFrate
(North)
Morris
(East)
3
5
14
9
37.5
62.5
60.9
39.1
4
5
8
10
44.4
55.6
44.4
55.6
7
Morrison
6
3
33
9
66.7
33.3
78.6
21.4
8
Parker
I
6
22
13
14.3
85.7
62.9
37.1
9
DeFrate
(North)
Morris
(East)
4
I
21
3
80.0
20.0
87.5
12.5
3
4
8
9
42.9
57.1
47.1
52.9
Morrison
5
I
27
6
83.3
16.7
81.8
18.2
_5
66
_2
52
_18
280
_1Q
149
71.4
28.6
64.3
35.7
55.9
a. i
65.3
3a 7
6
9
10
11
Parker
Totals
-
Table VIII.
36-
The effect of V a p a m , CBP and PCNB soil treatments on the
incidence of root rot in Janet variety of sweet peas in
1956.
Sweet Pea Plants
Numbers
Treat­
ment
Vapam
CBP
Plot
Percentage
Treated
H
D
Treated
Check
H
D
H
D
Taylor
Bole
0
4
36
48
22
22
42
75
0.0
7.7
100.0
92.3
34.4
22.7
65.6
77.3
Gaines
Hartman
9
7
15
13
46
41
27
8
37.5
35.0
62.5
65.0
63.0
83.7
37.0
16.3
DeFrate
(South) _ 6
26
Totals
i!
143
10
26*2
82*8
15 uk
8U.6
20*2
UU.6
69.7
141
22
175
9
83
14
75.0
25.0
85.6
14.4
27
35
16
87
59
24
21
197
29
42
28
43.8
5.4
61*9
56.2
94.6
38.1
67.0
36.4
52.5
33.0
iZ*5
113
46.6
53.4
63.5
36,5
36
21
57
34
18
52
20.0
68.7
80.0
52
154
21*2
64.2
82*8
35.8
16.2
1*9.1
50.9
74.8
25.2
Morrison 27
DeFrate
(North) 21
2
Parker
Ballard 26
Totals
PCNB
Check
H
D
Erwin
Morris
Totals
76
9
Jt6
55
61
63.6
-
37-
Percentage of
healthy plants
!OCX
90
Figure
5»
T h e e f f e c t of V a p a m , CBP,
o n the i n c i d e n c e of s w e e t
and PGNB
pea root
soil
rot*
treatments
38GENERAL DISCUSSION AND CONCLUSIONS
This study was undertaken in an attempt to better understand the
trouble encountered with raising sweet peas*
It was primarily initiated
to determine the causal organism and the,predisposing factors associated
w i t h the root-rot disease of sweet peas*
.Secondly, an attempt was made
at devising a comparatively safe and easy means of control for this dis­
ease*
There are a number of pathogenic organisms present in the soil
which are capable of attacking sweet peas*
Organisms such as Anhanomvceg„
.Rhizoctonia <, Thielavionsis« Pvthium and Fusarium may be present i n large
n u m bers, and according to reports are able to infect sweet pea plants*
.I n this study species of Fusarium were consistently isolated from rootrot-infected sweet peas, and these species were of numerous and diverse
types*
The occurrence of various strains of Fusarium differing in viru­
lence and pathogenicity on the same host further complicated the picture*
■These strains may range in virulence from saprophytic to severely patho­
genic*
The lack of uniformity of Fusarium in culture and in pathogenicity
has been observed on numerous occasions by.Oswald (17), Buxton (3), Snyder
(23) and Armstrong and Armstrong (I)*
Environmental factors, such as soil temperature and moisture, are
extremely important in determining the predominance of any one micro­
organism at any given time, as Smith and Walker (22) found in their work
with Aphanomvces*
Temperature is probably one of the factors of greatest
influence on FuSarium0
It appears that this fungus normally requires a
relatively high temperature for its growth and pathogenicity* .Morris and
"
39“
Nuttihg (14) found that Fusaria grew best at 20° to 22° C in culture.
Walker (23), Tisdale (27) and the results of this work show that this
group of fungi is more pathogenic at a .temperature of about. 28° Co
The possibility of. primary infection b y an organism which opens an
avenue of entrance for Fusarium
should be also considered <,
The pri­
mary infection may be caused b y Aphanomvces. Fvthium. Thielavioosis,.
and some other organisms *
In this study none of these organisms were
ever isolated from diseased roots.
Since Fusarium is a very rapid
grower, it quickly spreads throughout the host tissues when introduced.
.,In this w a y it may almost completely mask the primary organism or even
suppress its growth.
In nearly all of the isolations made in this
study, bits of tissue from the uppermost limits of the discolored vas­
cular tissues were used.
B y this procedure a faster growing organism
would have been obtained, and the primary, slower growing organism may
have been overlooked.
In all the greenhouse pathogenicity tests conducted in this study,
the soil was disinfected b y steam sterilisation and presumably all, or
nearly all, the soil microorganisms were destroyed.
This would practi­
cally eliminate the possibility of sweet peas being infected with any
other organism except Fusarium0
the soil in the field plots.
However this would not be the case in
The possibility that Fusarium may be only
'weakly pathogenic in absence of o t h e r 'microorganisms may give a partial
explanation for the low pathogen!city expressed by the strains of Fusaria
tested in sterile soil in the greenhouse.
When soil is brought to the high temperature (IlO0C) necessary for
-
40
-
"
sterilization, there is a likelihood of decided chemical changes in the
available nutrients*
This could influence the pathogenicity tests in
the greenhouse as both the organism and the plants are dependent on
these nutrients for their growth*
The pathogenicity test in the labora­
tory, on the other hand, was conducted with the organisms in an agar
block*
It is quite possible that the nutrients needed b y the organism
for limited growth were supplied b y the medium.
Tint (26) and Smith
and Walker (22) illustrated this point in their work with Fusarium and.
.
Anhariomyces ,,species *
The differences in soil^type and pH under which the field tests were
conducted m a y also give partial explanation for the differences in ef­
fectiveness of the chemical soil-treatment*
Orton (16) found that
»‘
Fusarium w i l t of cotton was more prevalent in light sandy soils.
Tint
(26) also found Fusarium more prevalent in light soils, and he states
that a soil pH of neutral or slightly acid is more conducive for develop­
ment of the organism.
It appears that additional work should be conducted on this pro­
b l e m to clarify the relationship of Fusarium to the root rot of sweet
peas,
A careful study should be carried out in respect to the possibi­
lity of a primary organism*
-
41“
SUMARY. .
1«
The nature of a sweet pea root-rot' disease .and methods of its control
were investigated in this study,
2.
Isolations of fungi were made from cortical and vascular tissues of
diseased sweet pea plants during the course of the study.
In all
cases species of Fusarium were obtained,
3»
Pathogenicity tests were conducted in the greenhouse with the
Fusarium cultures obtained.
Sweet peas were planted in pots of
sterile soil, which were later inoculated.
Three cultures of
Fusarium showed variable degrees of pathogenicity to sweet peas,
4,
A technique for testing pathogenicity in the laboratory was also
used.
This method consisted of growing sweet pea seedlings in test
tubes w i t h an agar block containing one of the Fusarium cultures.
The degree of pathogenicity expressed b y three cultures was compar­
able to the pathogenicity shown b y these cultures in the greenhouse
tests,
5,
A mixture of 12 cultures, including the three pathogenic ones, was
also tested for relative pathogenicity,
A moderate degree of
pathogenicity was expressed in this test,
6,
Three soil disinfecting materials were tested for controlling root
rot of sweet peas in garden p l o t s :
Vapam 4” S
(31%
sodium N-methyl-
dithiocarbamate), GBP (chlorobromopropene) and Terrachlor (PCNB /
'
20%
7,
pentachloronitrobenzene)„
GBP-treated.plots produced a consistently high percentage of healthy
plants w i t h 6£,3 and 63.5 for 1955 and 1956 respectively.
The check
-
42-
plots produced 5>5><>9 and 46*6 per cent healthy plants for the same
years*
8»
Vapam-treated plots produced 78.6 and U U »6 per cent healthy plants
and the checks produced 31 «U and
15>*U
per cent in 1955 and 1956
respectively.
9*
Plots treated w i t h Terrachlor had 74*8 per cent healthy plants as
compared w i t h U9 «1 per cent in the checks.
This compound was only
used in 1956.
10.
It appears that at least one type of root rot of sweet peas can be
caused b y Fusarium.
These results showed that this disease can be
at least partially controlled b y soil treatments.
-
43-
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1951.
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Root r o t o f sw e e t p e a s .
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